Processes for the recovery of uranium



United States Patent 3,347,642 PROCESSES FOR THE RECOVERY OF URANIUMThomas Garfield Thomas, Lea, near Preston, and Stanley GeorgeWilson,'Frodsham, near Chester, England, assignors to United KingdomAtomic Energy Authority, London, England No drawing. Continuation ofapplication Ser. No. 790,396, Fell). 2, 1959. This application Sept. 3,1964, Ser. No. 39 ,315 Claims priority, application Great Britain, Feb.17, 1958,

4 Claims (Cl. 23-342 This application is a continuation of applicationSer. No. 790,396, filed Feb. 2, 1959, and now abandoned.

This invention relates to the recovery of uranium values from magnesiumfluoride and calcium fluoride slags.

Uranium metal may be produced by interaction of uranium tetrafluoridewith either magnesium or calcium. One of the reaction products is then afluoride slag which may during cooling entrap droplets of uranium and/ordispersions of uranic materials which it is desirable to recover.

A known process for recovery of such uranium from magnesium fluorideslags is described in Chemical Engineering Progress (vol. 53, No. 2(February 1957) pages 56 59 and involves the following successive steps:

' 1) Roasting and fine-grinding of the slag;

(2) Leaching the roasted and finely-ground slag with hydrochloric acidto bring the uranium into solution;

(3) Precipitating the uranium from the filtered leach liquor asinsoluble uranyl ammonium phosphate;

(4) Converting the uranyl ammonium phosphate to a sodium di-uranate byinteraction with sodium hydroxide solution; and (presumably) (5)Conversion of this sodium di-uranate to a solution suitable for arefinery process. (In this step nitric acid liquor is treated instainless steel equipment, but in the absence of fluoride ions.)

It is thought that the known process described above was developed toavoid the serious corrosion problem which occurs when nitric acidleaching of fluoride slags is applied in stainless steel containers.

The present invention which has an object to provide a simpler and lessexpensive process for producing a solvent extraction refinery feed fromuranium containing fluoride slags is based on the discovery that bycontrol of nitric acid strength and more particularly temperatures, asatisfactory leaching of magnesium and calcium fluoride slags can takeplace in stainless steel vessels with an acceptable and predictablecorrosion rate.

According to the present invention magnesium fluoride of calciumfluoride, arising from the production of uranium from uranium tetrafluoride, is leached in stainless steel equipment with nitric acid sothat the acidity is finally between /2 normal and 5 normal, the leachbeing carried out at between 40 C. and 60 C. to bring substantially allthe uranium into aqueous solution. The solution may then be treated withany organic solvent suitable for uranium extraction in a known manner.

One way of carrying out the process of the invention will now bedescribed in more detail in the particular case of magnesium fluorideslag and with tributyl phosphate as the organic solvent.

Magnesium fluoride slag is crushed to approximately A in. size andground in .a wet ball mill sufliciently for 98% to pass a 60 mesh B.S.S.sieve. The use of the wet grind avoids hazards arising from dust orfire. The mill product slurry is preferably 70% solids by weight, and isthen leached by admixture with 60% w./-w. nitric acid (i.e. l3-normalacid) for a period of 12 hr. while the temperature is maintained at 60C. The final acidity of the aqueous phase of the leach slurry becomes l/z-normal by virtue of the predetermined relative proportions of acidand mill slurry used and no need arises to bring about concentration byboiling which would cause bad corrosion. An acidity of lower than/z-normal and a temperature of lower than 40 C. does not securesatisfactory extraction of uranium. This leach is carried out in astirred container made of austenitic stainless steel containingapproximately 18% chromium, 8% nickel and 1% titanium, suitably weldedand heat-treated. It may be an advantage then to add lime or some otherconvenient base to neutralise part of the remaining acidity and toconvert the said part of the acidity to, for example, calcium nitrate.The leach slurry is then filtered and the solids are washedsubstantially free from uranium. It may be an advantage to make anaddition of a conditioning or flocculating agent beforehand if the leachslurry contains a proportion of fines which would otherwise impair thefiltration. We have found Separan 26 10 (reg. trade mark) to beeffective for this purpose. It may then become possible to separate upto 40% by volume of the liquid phase by simple decantation so thatfiltration need only be made for the remainder. The filtrate with orwithout any decantate and with or without any washings is then contactedwith 20% v./v. tributyl phosphate dissolved in odonrless kerosene toextract the uranium according to known methods.

The fluoride content of the aqueous phase is not" sufficient at thetemperature used to cause excessive corrosion of the stainless steelcontainer nor to impair the solvent extraction of uranium to asignificant extent. We have found the aqueous phase to contain typical 4gm. of fluorine per litre and 40 milligrams of nickel per litre, part ofwhich nickel will have been derived from the slag and only the remainderfrom corrosion of the stainless steel leaching equipment. If the finalconcentration of nitric acid is excessive it may be extracted by thesolvent in undue degree in preference to the uranium though in theexample we give this is not marked at acidities of below 5-normal.Nitrates of the commoner bases are not usually extracted by the uraniumsolvents to any substantial degree and are on the contrary usuallybeneficial in promoting the desired extraction of uranium.

We claim:

1. A method of leaching uranium from a fluoride slag arising from theproduction of uranium from uranium tetrafluoride using nitric acid aloneas the leaching agent said method comprising the steps of providing astainless steel container, mixing nitric acid with slag in thecontainer, the nitric acid being used in predetermined amounts adaptedto achieve a final and total acidity of /2 normal to 5 normal in respectof nitric acid only, and heating the slag and acid in contact with thecontainer to a temperature in the range 40 C. to 60 C. there'by bringinguranium into aqueous solution with acceptable corrosion of the stainlesssteel container.

2. A method of leaching uranium from a fluoride slag perature in therange 40 C. to 60 C. thereby bringinguranium into aqueous solution withacceptable corrosion of the stainless steel containers.

3. A method of leaching uranium from a fluoride slag arising from theproduction of uranium from uranium tetrafluoride using nitric acid aloneas the leaching agent said method comprising the steps of providing astainless steel container, mixing nitric acid with slag in thecontainer, the nitric acid being used in predetermined amounts adaptedto achieve a final and total acidity of /2 normal to 5 normal in respectof nitric acid only, and heating the slag and acid in contact with thecontainer to a temperature in the range 40 C. to 60 thereby bringinguranium into aqueous solution with acceptable corrosion of the stainlesssteel container at fluoride levels of about 4 grams of fluorine perliter of said aqueous solution.

4. A method of leaching uranium from a fluoride slag arising from theproduction of uranium from uranium tetrafluoride using nitric acid aloneas the leaching agent said method comprising the steps of providing astainless steel container, mixing nitric acid with slag in thecontainer, the nitric acid being used in predetermined amounts adaptedto achieve a final and total acidity of /2 normal to 1 /2 normal inrespect of nitric acid only, and heating the slag and acid in contactwith the container to a temperature in the range 40 C. to 60 C. therebybringing uranium into aqueous solution with acceptable corrosion of thestainless steel containers at fluoride levels of about 4 grams offluorine per liter of said aqueous solution.

No references cited.

BENJAMIN R. PADGE'IT, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner.

1. A METHOD OF LEACHING URANIUM FROM A FLUORIDE SLAG ARISING FROM THEPRODUCTION OF URANIUM FROM URANIUM TETRAFLUORIDE USING NITRIC ACID ALONGAS THE LEACHING AGENT SAID METHOD COMPRISING THE STEPS OF PROCIDING ASTAINLESS STEEL CONTAINER, MIXING NITRIC ACID WITH A SLAG IN THECONTAINER, THE NITRIC ACID BEING USED IN PREDETERMINED AMOUNTS ADAPTEDTO ACHIEVE A FINAL AND TOTAL ACIDITY OF 1/2 NORMAL TO 5 NORMAL INRESPECT OF NITRIC ACID ONLY, AND HEATING THE SLAG AND ACID IN CONTACTWITH THE CONTAINER TO A TEMPERATURE IN THE RANGE 40*C. TO 60*C. THEREBYBRINGING URANIUM INTO AQUEOUS SOLUTION WITH ACCEPTABLE CORROSION OF THESTAINLESS STEEL CONTAINER.
 3. A METHOD OF LEACHING URANIUM FROM AFLUORIDE SLAG ARISING FROM THE PRODUCTION OF URANIUM FROM URANIUMTETRAFLUORIDE USING NITRIC ACID ALONE AS THE LEACHING AGENT SAID METHODCOMPRISING THE STEPS OF PROVIDING A STAINLESS STEEL CONTAINER, MIXINGNITRIC ACID WITH SLAG IN THE CONTAINER, THE NITRIC ACID BEING USED INPREDETERMINED AMOUNTS ADAPTED TO ACHIEVE A FINAL AND TOTAL ACIDITY OF1/2 NORMAL TO 5 NORMAL IN RESPECT OF NITRIC ACID ONLY, AND HEATING THESLAG AND ACID IN CONTACT WITH THE CONTAINER TO A TEMPERATURE IN THERANGE 40*C. TO 60* THEREBY BRINGING URANIUM INTO AQUEOUS SOLUTION WITHACCEPTABLE CORROSION OF THE STAINLESS STEEL CONTAINER AT FLUORIDE LEVELSOF ABOUT 4 GRAMS OF FLUORINE PER LITER OF SAID AQUEOUS SOLUTION.